This invention relates to ink rollers used for supplying ink to a face of a type or the like in a printer such as desk calculator, electronic computer, register and so on. This invention also relates to a method of producing the same.
In order to supply ink to the face of type or the like in a printer such as desk calculator, electronic computer, register, teletypewriter, typewriter and so on, the ink roller should desirably have a satisfactory ink-impregnation ability and a high ink-holding ability to prevent not only dripping of the ink in use but also the occurrence of blotting on paper. Further, the ink roller is required to supply a proper quantity of the ink to the face of the type without the uneven contact.
As an example of an ink roller of this type, there have hitherto been proposed ones made from compression bodies of flexible polyurethane foams. However, ink rollers satisfying all of the above requirements, particularly ink rollers having a long length (axial length) are not provided at present.
Moreover, when the ink roller is made from the compression body of the flexible polyurethane foam, it is cut out from the compression body along a direction perpendicular to the compression direction of the compression body. If the above ink roller is impregnated with an ink, it unevenly swells in its radial direction. As a result, the sectional form thereof produces an eccentricity from a true circle. In the production of the ink rollers, therefore, it is necessary to cut out the ink roller from the compression body in such a manner that the compression direction of the compression body is coincident with the axial direction of the ink roller.
In the conventional compression body of the flexible polyurethane foam, the permanent deformation is obtained by hot pressing the flexible polyurethane foam in a certain compression direction. However, the resin constituting the skeleton of the flexible polyurethane foam is low in the heat conductivity, so that heat transfer from a heat plate is poor during the hot pressing. Particularly, when the length in the compression direction of the flexible polyurethane foam is long, heat is not sufficiently transferred to the central portion of the foam. Further, the diameter of interconnected voids in the usual foam is small, so that the convection heating of air can hardly be expected. As a result, a large temperature gradient is produced in the flexible polyurethane foam during the hot pressing. Therefore, the resulting compression body produces a gradient of hardness or compressibility in its compression direction, a degree of which particularly becomes larger in case of the compression body having a large thickness in the compression direction. In this connection, there has been attempted techniques to rise the heating temperature or continue the heating over a long time to sufficiently heat the central portion of the flexible polyurethane foam during the hot pressing. But, in this case the heated surface portion of the compression body is degraded to such an extent that the compression body cannot be practically used.
Thus, it is very difficult to produce uniform ink rollers, particularly ink rollers having a long length (axial length) from such compression bodies. On the other hand, there are obtained only ink rollers having a relatively short axial length of about 10-15 mm, which is coincident with a width of a ribbon used in a typewriter.
There is a demand to produce large-size ink rollers with the advance of high-speed printing process in line printers or the like. Particularly, it is desired to develop uniform ink rollers having a length of not less than 20 mm and satisfying all of the aforementioned requirements. In electronic disk calculators and electronic cash registers wherein the ink roller is directly struck by a head of a type, for instance, it is required that the length of the ink roller is coincident with a width of the figures to be displayed. In the later case, the ink roller is required to have a length of more than about 50 mm, which is fairly longer than the conventional roller, and to be uniform.